1. Field of Invention
The present invention relates to an electrical connection box which is suitable to be mounted on a vehicle, particularly an electrical connection box to which a high voltage is to be applied, and to a vehicle having such a box installed.
2. Description of Related Art
Normally one secondary, i.e. rechargeable, battery having a rated voltage of 12V and a maximum nominal voltage of 14V is mounted on an automobile of the internal combustion engine type. A voltage up to the maximum voltage of 14V is applied from the battery to a circuit composed of bus bars and the like that are accommodated in an electrical connection box. The power supply is distributed by the internal circuit of the electrical connection box. The operation of electric/electronic component parts mounted on the vehicle is controlled through electric wires connected with the internal circuit.
On a goods vehicle, such as a lorry or truck, a rated voltage of 24V and a maximum voltage of 28V are applied to a circuit by a battery structure.
In recent years, electric/electronic component parts have been mounted in increasing numbers on a vehicle, and there is an increase in the electric current which is applied to one electric/electronic component part. For example, the electric power required to drive a fan is conventionally 130 watts, but has become 260 watts in recent years. At the rated voltage of 12V of the battery, it is impossible to operate suction and exhaust devices of an engine, electromotive power steering, and the like devices, requiring a high voltage such as 36V. Therefore, they are mechanically operated by the driving force of the engine.
With the increase of the electric current applied to each electric/electronic component part, the diameter of the electric wires used has become larger. Further, with rapid increase of the number of electric/electronic component parts, the number of electric wires has increased recently, which has increased the diameter of a wire harness having a bundle of electric wires. Consequently, the weight of the electric wires to be wired on a vehicle body has increased.
As described above, if the power supply from the battery is incapable of operating the suction and exhaust devices of the engine, they are mechanically operated. In this case, it is impossible to accomplish fine control of the operation of the suction and exhaust devices. Further, much fuel is consumed, which pollutes the environment. Accordingly, it is preferable to operate the suction and exhaust devices of the engine and the like not mechanically but electrically by the power supply from the battery.
In the case where the circuit is so constructed that a voltage higher than 14V can be applied to the circuit of the electrical connection box composed of bus bars and the like, it is possible to reduce the required electric current and thus the diameter of the electric wires and the size of a bundle of a plurality of electric wires (wire harness). Therefore, it is possible to reduce the weight of the electric wires.
Further, with the application of a high voltage to a circuit composed of bus bars and the like, it is possible to control the operation of the suction and exhaust devices, the power steering motor, and the like not mechanically or hydraulically but electrically. In this case, it is possible to accomplish fine control of the operation of suction and exhaust devices and the like. Further, fuel consumption can be reduced, which reduces pollution.
It is preferable to apply a high voltage of about 42V to the electromotive power steering motor, the suction and exhaust devices of the engine, the fan, and other devices requiring a high voltage. On the other hand, in an automobile, it is preferable to apply the rated voltage of 12V (maximum voltage: 14V) to signal-generating devices of the electric/electrical component parts and coils of relays.
Water is liable to penetrate into terminal recesses of a relay accommodation structure at the exterior of an electrical connection box mounted in a vehicle from a wall partitioning the recesses from each other. In the case where a circuit to which a high voltage of for example about 42V is applied is connected to a relay mounted in the relay accommodation structure, a leak current is liable to be generated between terminals of the relay to which the high voltage of, for example, about 42V is applied. This is because water penetrates into a positive (+) terminal insertion portion of the relay accommodation part and a negative (xe2x88x92) terminal insertion portion thereof from a partitioning wall partitioning them from each other. From there, water may also penetrate into the box to cause leak currents between bus bars.
Therefore, it is an object of the present invention to reduce or avoid the risk that water penetrates into the terminal recesses or into a gap between high-voltage bus bars from a relay accommodation part to thereby prevent a leak current from being generated, particularly in the case where an electrical connection box is provided with a circuit to which a high voltage is applied.
According to the present invention, there is provided an electrical connection box having a casing having an upper wall, at least one bus bar which is mounted within the casing and to which in use a nominal maximum voltage of not less than 14V and not more than 200V is applied and, on the upper wall of the casing, a relay accommodation structure adapted to receive in use at least one electrical relay and comprising upstanding walls defining at least a first recess at which a positive terminal of the relay is to be inserted and a second recess at which a negative terminal of the relay is to be received, the first and second recesses being partitioned from each other by one of the upstanding walls which has an upper edge at which an inclined groove is provided for carrying away water by gravity.
With this construction, water which lodges on the upper edge of the partition wall partitioning the respective terminal insertion recesses of the relay accommodation structure flows into the inclined groove and moves by gravity to the exterior of the relay accommodation structure. Accordingly, it is possible to reduce or prevent water from penetrating into the positive (+) or negative (xe2x88x92) terminal insertion recesses. Consequently, it is possible to prevent the water from penetrating into gaps between the high-voltage bus bars.
The groove may be formed on the upper edge or end surface of the partition wall so as to slope in one direction only along the wall between the terminal insertion portions, or may have a higher central portion and extend linearly downward in two directions to the exterior of the relay accommodation part. That is, it is preferable to configure the groove in such a way that water which lodges on the partitioning wall flows linearly downward through the groove to the exterior of the relay accommodation part.
It is preferable that the high voltage to be applied to the high-voltage bus bar is at least about 28V, particularly about 42V. In this case, it is easy to provide the voltage applied to the high-voltage bus bar at 42V by connecting in series three batteries each having a rated voltage of about 12V (nominal maximum voltage: 14V) generally used in automobiles. Needless to say, it is possible to use a single battery having a maximum voltage of about 42V. The reason why the high voltage to be applied to the high-voltage bus bar is set to about 42V is partly because using a voltage close to or above 50V for the high-voltage bus bar may be dangerous. The present inventors have conducted salt water experiments in order to ascertain the degree of risk when applying a voltage of 42V in an electrical junction box suitable for use in an automobile engine compartment. The experiments were done as follows:
1 ml of salt water was injected into each terminal hole of the casing of a junction box which had bus bars disposed inside. Electrical components such as relay, fuse, connectors, etc. were mounted on the casing. A voltage of 42V was applied to bus bars of the junction box for 8 hours and then suspended for 16 hours. This was repeated twice. There was initially no change to the bus bars and electrical components. After the third repetition, it was found that extra electric current passed between the bus bars generating heat and a portion of bus bars was melted. The heat also melted resin around bus bars such as an insulation plate, casing and resin portion of electrical components adjacent the casing.
Accordingly, since damage did not occur until after the third exposure to salt water, it was confirmed that in consideration of conditions under normal use of an automobile, the application of the electric power at 42V to the electric/electronic component parts should not cause a problem.